The optical elements such as an optical fiber, a Laser diode and a Photo diode et al. are required to be connected to one another with a high grade of accuracy. Otherwise, the light transmission efficiency is deteriorated. For the purpose, various types of optical connectors were developed. Since most of them use a lense or the like to adjust the optical parts thereof, however, they were not necessarily convenient to employ, in addition to that the degree of accuracy achievable by the optical connectors is not necessarily satisfactory. Developed to remove the drawbacks is a module on which plural optical elements such as an optical fiber, a Laser diode, a Photo diode et al. can be arranged in one action with a high grade of accuracy to secure a continuous optical path for the plural optical elements to allow them to transmit light signals.
Production of the module is based on the technology prevailing for production of semiconductor devices e.g. photo lithography processes, processes for etching a specific semiconductor substrate or layer, processes for depositing a specific metal layer on a semiconductor layer et al. Thus, such a module is usually called a V-groove substrate. In this specification, this nomenclature is employed.
Referring to FIG. 1, a brief description to a V-groove substrate available in the prior art will be presented below. A V-groove (7) is produced along the top surface of an Si substrate (1) covered by an SiO.sub.2 layer (8). An optical fiber (14) is arranged in the V-groove (7) whose surface is covered by an SiO.sub.2 layer (8) as well. The core (15) of the optical fiber (14) extends in a horizontal direction towards a Laser diode or Photo diode (13) arranged opposite to the core (15) of the optical fiber (14). The anode wiring (16) and the cathode wiring (17) of the Laser diode or Photo diode (13) are arranged on the top surface of the Si substrate (1). In this example, a monitor photo diode (18) is arranged opposite to the Laser diode or Photo diode (13). The anode wiring (19) and the cathode wiring (20) of the monitor photo diode (18) are arranged on the top surface of the Si substrate (1) as well.
In the V-groove substrate available in the prior art, it is still important to align a Laser diode or a Photo diode with an optical fiber with a dimensional accuracy of .+-.1 .mu.m. Otherwise, the optical axis of a Laser diode or of a Photo diode can not be aligned with the core of an optical fiber.
Since an anisotropic etching process conducted employing a KOH solution is inevitably accompanied by side etching in which the ratio of the side etching versus the vertical etching is as large as approximately 0.3, it is not easy to align an optical element with a finished V-groove, resultantly causing a dissatisfactory grade of alignment accuracy for the optical elements and an optical fiber.
Further, it is recognized that the longitudinal edges (an edge along or parallel to the axis of a V-groove) of a V-groove produced employing a KOH solution is inclined to go zigzag or meander. This is one of the reasons to make the alignment an optical element with an optical fiber difficult. Thus, it is very convenient, if such a meander or the linearity of the edges of a V-groove can be found during the process for producing the V-groove.